1. Field of the Invention
The present invention relates to a tire vulcanizer, and particularly, to an arrangement in which a movable upper mold is vertically moved and opened and closed relative to a fixed mold and a ball-screw shaft construction is used as a vertically moving and opening and closing means, in which arrangement the safety and durability of the opening and closing mechanism are increased and smooth motion is rendered possible to effect. The invention further relates to an improvement in a slide guide construction for moving the upper mold up and down in the tire vulcanizer.
2. Description of the Prior Art
As is known, in a tire vulcanizer of the divisional mold type, a lower mold is secured onto a base of the vulcanizer and an upper mold supported by a top link or other carrying member is made openable and closeable relative to the lower mold to thereby facilitate a series of vulcanizing and molding operations such as charging and setting green tires, vulcanizing and molding with the upper and lower molds closed and clamped and delivery of vulcanized tires. As means for opening and closing the upper mold relative to the lower mold there are used various known mechanisms. However, the ball-screw shaft construction has been put to practical use recently in place of usual practices such as gears provided by making use of the side frame of the vulcanizer, a mechanically opened and closed mechanism in which an upper mold support beam or a top link is moved by the side link connected to the gear, and a hydraulically opened and closed mechanism in which the upper mold support beam or top link is moved by use of a hydraulic cylinder. In this construction, the screw shaft is reversibly provided by making use of a vucanizer side frame stood upright on the base with the lower mold on the vulcanizer base sandwiched therebetween, a threaded nut is threadedly engaged with the screw shaft through a ball (e.g. a steel ball) whereby the threaded nut is moved up and down under the interposition of a ball rolled in a threaded groove through the reversible rotation of the screw shaft, and the threaded nut is integrally connected with the upper mold support beam or top link whereby the upper mold is vertically moved relative to the lower mold for opening and closing. A motor with a brake is used as a driving source for reversibly rotating the screw shaft. The opening and closing mechanism of the ball-screw shaft construction has excellent merits in that essential construction thereof is compact, the efficiency of energy is good, and troubles such as a leak of liquid-pressure fluid in the hydraulic type and deterioration caused by high heat at vulcanization whereas since the opening and closing mechanism is totally of a rigid construction, there poses a new problem relative to necessary motion in the tire vulcanizer. That is, after the upper mold has been closed completely relative to the lower mold by the rotation of the screw shaft and by the downward movement of the threaded nut, it is necessary to clamp both the molds by a separate well known means in order to resist internal pressure upon vulcanization and molding. As that time, the upper mold is further pulled down through a few strokes towards the lower mold by means of a separate fastening means with the brake of the motor with a brake released to carry out pressing and clamping operation. Although the aforesaid pull-down stroke is not great but the screw shaft is reversed by axial thrust when the brake is released during that stroke. The clamping operation is carried out in a short period of time and the screw shaft system will have a large mass resulting from a connecting shaft in an interlocking relation with the screw shaft, a reduction gear in interlocking relation with the connecting shaft, a motor with a brake and the like, and therefore, a time-lag occurs in connection with the clamping operation, and an excessive external force is exerted on parts of the screw shaft opening and closing construction, such being of a rigid construction. There is also a possibility that in the mold opening and closing operation, when the upper and lower molds come into abutment with each other to produce a shock, the ball-screw shaft construction cannot at all absorb such a shock because the construction is of a rigid construction, and ball-screw shaft construction tends to be damaged and the durability thereof is materially shortened. Particularly, in the tire vulcanizer, the upper mold has a considerable weight including assembly constructions including a thermal board (a support platen), a heat insulating material and the like. In addition, most of vulcanizers not only include a mere set of divisional molds but is of a multiple type in which at least two sets of or more divisional molds are supported on the side of a common beam or top link, and therefore, loads of heavy articles are applied to the threaded nut and the whole screw shaft. Thus, the excessive motion as described above greatly affects the durability of the opening and closing mechanism and safety due to failure to expect smooth motion operation as normally occurs in hydraulic operation.
As is also known, in the tire vulcanizer which uses the divisional mold, a lower mold is secured to a vulcanizer base and an upper mold is held on a slide vertically movably supported on a fixed frame such as a column or the like stood upright on the base, whereby the upper mold is opened and closed relative to the lower mold through upward and downward movement of the slide to effect delivery and the setting of green tires on the lower mold and vulcanization and molding of tires between both divisional molds through closing and clamping of the upper mold. At this time, in motion of the slide which is moved up and down while holding the upper mold, the parallelism of the slide with respect to the base is properly maintained and deviation in the center of the molds is minimized, when the slide is moved up and down to enhance the vulcanizing accuracy and prolong the service life of the molds by registration of the upper and lower molds, which are requirements for such motion of the slide. In the past, therefore, a guide having a vertical guide surface has been provided on the side of a fixed frame such as a column, and an end of the slide brought into engagement with said guide to control upward and downward movement thereof. On the other hand, in the tire vulcanizer, heating sources are housed in both the molds for vulcanization and molding and in addition, steam or other heating medium is supplied into the tire. Therefore, the slide portion undergoes thermal expansion due to propagation of such thermal energies. It is necessary to provide beforehand a clearance between the slide surface of the slide and the guide surface of the guide. If this clearance is smaller than the amount of thermal expansion, execessively high surface pressure is produced between the slide surface and the guide surface and therefore burning tends to occur during sliding due to repetitious upward and downward movement. If the clearance is provided largely to avoid an occurrence of such problem, poor parallelism of the slide lower surface to the base surface and deviation from the center position tend to occur, leading to difficulties such as lowering of vulcanization accuracy, shortening of the service life of molds and the like. This drawback is inherent in the conventional type of rigid construction which merely comprises the slide and the guide.